Ink-jet printing is a technology that uses small drops of fluid, such as ink, to form an image on a medium, such as paper, film, transparencies, and cloth to name a few. At least two types of ink-jet printing exist, continuous flow and drop-on-demand. Continuous flow ink-jet printing uses electrostatic acceleration and deflection to select ink drops from a constant flow of ink to form an image. Drop-on-demand inkjet printing has at least two forms, piezoelectric and thermal. Piezoelectric ink-jet printing uses a mechanical energy dissipation element to eject ink. Thermal ink-jet printing uses a resistive energy dissipation element to eject ink using heat energy. This heat energy vaporizes a thin layer of ink to form a bubble that ejects a small drop of ink through a nozzle. Forming a group of nozzles into an array on a substrate creates a printhead. As the ink leaves a nozzle in the printhead, the capillary action caused by the surface tension of the fluid within the nozzle pulls fresh ink back into the nozzle. This process is repeated thousands of times per second.
The physical components needed to implement thermal ink-jet technology are embodied in a print cartridge which contains the printhead, an ink supply and a pressure regulator for the ink supply. Different print cartridge body designs exist, each optimized to operate for a particular type of printing to be performed. Within the print cartridge is an ink delivery system used to provide pressure regulation and to supply ink from a container or reservoir to the printhead. Some examples of ink delivery systems are a rubber bladder, a foam block, a spring bag, and a bubble generator with an internal spring bag, to name a few. The printhead typically is formed by the application of thin or thick films onto a substrate. The substrate traditionally is a glass or silicon substrate but other suitable substrate materials are known to those skilled in the art.
Within the print cartridge is the container used to store the ink supply or a portion of a larger ink supply which may be stationary. The ink traditionally is either dye-based or pigment based. A dye-based ink typically provides the most vibrant colors and the widest color gamut. A pigment-based ink generally has enhanced water and light fastness, which enable outdoor signage and other applications. New applications for ink-jet printing require fluids other than ink. One such application is the layering of a protective coating over a previously recorded medium to increase the water or light fastness.
When ink is ejected from a printhead nozzle with a drop-on-demand system, it is typically done one drop at a time. An ejected drop of ink is characterized by its velocity, trajectory, volume, aerosols (stray spray), and tail. The ejected ink drop characteristics are correlative with the resulting image quality perceived by a user. Another aspect of the perceived quality is resolution of the ejected drops. As resolution increases, the volume of the ejected drops are typically reduced.
Further, when creating a higher resolution of an image at the same or comparable page print speed as now done for lower resolution images, the repetition rate of ejecting ink from the printhead increases. Increasing the repetition rate requires that more energy over time be applied to the energy dissipation elements in the printhead, thereby causing the printhead to become hotter due to residual heat. If the printhead becomes too hot, the drop of ink will not be ejected from the printhead with the desired velocity and trajectory. Further, the aerosols may become a large spray resulting in poor print quality or vapor lock may occur causing a misfire. Vapor lock is caused by a large bubble ejecting all ink from the nozzle (depriming the nozzle), thus not allowing the capillary action to draw more ink back into the nozzle. In addition, just as a fuse blows when it is overloaded, the energy dissipation elements may be damaged from the residual heat resulting in a printhead that no longer functions properly. This type of catastrophic failure is a great inconvenience to a user as the print cartridge has to be replaced.
To support the higher repetition rates, new efficient fluid paths have been developed. Some developments have resulted in energy dissipation elements that are suspended over the ink supply without backing from the substrate. In these developments, the substrate has an channel opening in which ink is conducted from the ink supply to the printhead nozzles. This substrate channel opening is where the energy dissipation elements are suspended. While this efficient path promotes quick refilling of the nozzle, thus allowing for increased repetition rates, residual heat left over in the energy dissipation elements after ejecting ink is unable to be properly dissipated into the substrate and ultimately into the ink supply. Further, as the density of the number of nozzles on a printhead increases to meet higher resolution goals, this residual heat is clustered into a more confined area than on conventional printheads. Some possible solutions have resulted in adding heat sinks to the printheads to help eliminate the residual heat. These approaches of adding a heat sink, nonetheless, increase the cost of the printhead.
However, due to increased competition from competitors and other technologies, the future of ink-jet printing lies in its versatility and its ability to continue to deliver high-quality color output at lower cost with higher reliability. Therefore a solution to the generation of residual heat must not only be low-cost, it must also support the need for increased reliability at even high density photographic quality color printing. A need thus exists to remove this excess residual heat as inexpensively as possible in order to meet a user's increased expectation of higher quality at a lower cost.